This invention is broadly applicable to controlling one or more electric motors driving a motor vehicle. It has particular utility as it relates to a Plug-in Hybrid Electric Vehicle (PHEV), and specifically to conversion of existing Internal Combustion (IC) engine vehicles into PHEVs, as described in U.S. Patent Application US 2007/0169970 A1, filed Jul. 26, 2007 “Electric Hybrid Vehicle Conversion” and U.S. Patent Application US 2009/0000836 A1 filed Jun. 27, 2008 “Balanced Belt or Chain Drive for Electric Hybrid Vehicle Conversion”. The function of this invention is to control one or more DC electric motors to propel a vehicle, either together with the existing IC engine as a parallel hybrid, or solely by electric power as a “strong hybrid”.
Kyle in U.S. Patent Application US2006/0030450 A1, Feb. 9, 2006, discloses a conversion of a conventional IC engine vehicle to an IC-electric hybrid vehicle with a control system having inputs of vehicle speed, throttle position, engine speed and electric motor speed to perform a complicated control operation on the electric motor, but with no details of how this is to be accomplished.
Hamstra and Gehrs in U.S. Patent Application US2007/0284164, Dec. 13, 2007, disclose a control system similar to the one of this invention but operated in an entirely different way due to the limitations of the motor they employ.
It is an objective of this invention to maximize the contribution from an electric storage battery to propelling a vehicle. It does this by using the electrical propulsion system to provide its maximum contribution until the storage battery is exhausted. Series wound traction motors are particularly good at starting heavy loads from a standing start and continuing to propel them up to high speeds without the need for shifting gear ratios, as is required by an IC engine with its limited operating speed range. The control system of this invention facilitates operating the electric motor in this mode, while maintaining operation of the IC engine as a back up to provide reversing in those cases when the electric motors are not electrically reversible, to drive the auxiliaries such as air conditioning, power steering and power brakes, and to provide 12 Volt battery charging. The IC engine is also available to provide extra power for acceleration and hill climbing and additional range when the batteries are exhausted.
It is an additional objective of this invention to sense when the batteries are exhausted and to prevent excessive current drain which will shorten their life.
It is yet another objective to provide a driver interface for a vehicle converted into a plug hybrid by the teachings of U.S. Patent Application US2007/0169970 A1, Jul. 26, 2007, which provides a driving experience substantially the same as before the vehicle was converted, so that the boost from the electrical system is transparent to the driver. The vehicle is operated in the same way whether electric power is available or not.